The present invention relates to the treatment of bacteria contaminated subterranean formations, and more particularly, to methods of treating bacteria contaminated subterranean formations to substantially reduce or eliminate such contamination using tri-n-butyl tetradecyl phosphonium chloride (TTPC).
A biocide is a chemical substance capable of killing living organisms, usually in a selective way. Biocides are commonly used in medicine, agriculture, forestry, and in industry where they prevent the fouling of water and oil pipelines.
Biocides, also called bactericides or antimicrobials, are used in oil and gas production. Their aim is to kill microorganisms, especially bacteria, or interfere with their activity. Microorganisms in oilfields or in injection water are generally classified by their effect. Sulfate-reducing bacteria (SRBs), denitrifying bacteria (hNRB), slime-forming bacteria (NR-SOB), yeast and molds, and protozoa can be encountered in nearly any body of water present in and around an oil field. Bacteria may be found in solution (planktonic), as dispersed colonies or immobile deposits (sessile bacteria). Bacteria can use a wide variety of nitrogen, phosphorus, and carbon compounds (such as organic acids) to sustain growth. Nitrogen and phosphorus are usually sufficiently present in the formation water to sustain bacterial growth but injection of organic nitrogen- and phosphorus-containing chemicals in fluid inserted into the formation can further increase growth potential.
Bacteria in oilfield water can be aerobic or anaerobic. One known type of anaerobic bacteria are SRB (desulfovibrio) bacteria, which are present in nearly all waters handled in oilfield operations. SRB convert sulfate ions into hydrogen sulfide—leading to reservoir souring. SRB can also produce sludge or slime, which can reduce the porosity of the formation. Hydrogen sulfide is acidic and can in turn cause sulfide scales, most importantly, iron sulfides. In addition, it is often necessary to remove hydrogen sulfide from gas prior to sale. Solid deposits of bacterial colonies are called “biofilms” or “biofouling.” The presence of iron sulfide or an increase in the water soluble sulfide concentration in a flow line is a strong indicator of microbially induced corrosion (MIC); therefore it is very important to prevent the formation of biofilms on the surfaces of flow lines and other production equipment. It is similarly important to have viable treatment strategies for both planktonic and sessile bacterial numbers. The potential for SRB activity is greater in the case of produced water reinjection (PWRI). Water that is reinjected can be a mixture of produced water and seawater. In such cases one had a mixture of SRB nutrients including sulfate ions, organic carbon, and nitrogen (often bound in ammonium compounds). There are SRB that can survive extremes of temperature, pressure, salinity, and pH but their growth is particularly favored in the temp range of about 40° F. to about 175° F.
When the fluids used in drilling or stimulating oil or gas wells contain bacteria, the producing formations can become contaminated with the bacteria. Such contaminated formations which have been fractured have heretofore been particularly difficult or impossible to treat. That is, prior attempts to introduce one or more bactericides into such formations to contact and kill the bacteria therein have been largely unsuccessful due to the bacteria being located in or near fractures at long distances from the well bores. When treating fluids containing bactericides have been pumped into such previously fractured contaminated formations, the treating fluids have either failed to reach the locations of the bacteria, and/or the proppant materials in the previously formed fractures have been disturbed thereby reducing the productivities of the formations.
In order for a biocide to be compatible and effective, it should be stable, and preferably, it should not react with or adversely affect components of the treatment fluid or formation. Incompatibility of a biocide in a well bore treatment fluid can be a problem, leading to treatment fluid instability and potential failure. Biocides may comprise quaternary ammonium compounds, chlorine, hypochlorite solutions, and compounds like sodium dichloro-s-triazinetrione. An example of a biocide that may be used in subterranean applications is glutaraldehyde.
By the present invention, improved methods of treating previously fractured bacteria contaminated subterranean formations are provided whereby the bacteria are substantially eliminated without lowering the productivities of the formations.